1. Field of the Invention
The present invention relates to an external stowage unit for a payload such as a weapon, countermeasure or unmanned underwater vehicle (UUV). It also relates to marine vessels incorporating such a stowage unit, and in particular, submarines incorporating such a stowage unit.
2. Summary of the Prior Art
Stowage units are known for storing weapons or countermeasures on marine vessels. Such units typically include an openable container for holding the weapon or countermeasure which, when closed, forms a ‘dry volume’ that protects the contents from the external environment. In some instances the container is mounted within a larger volume such that it can move within the larger volume. Such ‘shock-mounting’ shields the stowed weapon or countermeasure from impulsive accelerations. An embodiment of this concept is the ‘tube within a tube’ where a conventionally sized torpedo tube is shock-mounted within a larger tubular volume.
Deployment of the weapon or countermeasure can affect the buoyancy of the marine vessel incorporating the stowage unit. Prior to deployment the dry volume may be equilibrated with the ambient environment which, during submerged operation of the stowage unit, involves water displacing the gas occupying the dry volume. On release of the weapon or countermeasure, the overall mass of the stowage unit is reduced by an amount corresponding to the deployed weapon or countermeasure.
It is important that deployment of the payload does not adversely affect the buoyancy of the vessel. In vessels where the stowage unit is located internal to the waterproof hull, the changes in buoyancy caused by deployment can be compensated for by channelling the displaced gas into the watertight compartment and transferring a weight of water equivalent to the deployed payload from the external environment into the watertight compartment.
Internal placement of the stowage unit necessitates penetration of the watertight hull. External placement of the stowage unit may also require penetration of the watertight hull. The structural integrity requirements of the watertight hull often constrain the operation and positioning of weapon stowage units that penetrate it. This can lead to a sub optimal solution for both the vessel and the stowage unit. This is a particularly important consideration in the design of submarines, where the watertight hull (the ‘pressure hull’) must be able to resist a higher hydrostatic pressure than that experienced by surface vessels.